by Tim Jackson tim@FocusTestChart.com
Version 1.0 (This version was previously known as “Version: Sunday 6 June 2004”) There is NO change to this version other than the version numbering scheme. The latest version is always available at http://md.co.za/d70/focus.pdf
What is back focus? Back focus is when you shoot a pic like this one, expecting to get the resultshown on the left but, instead, you get the one on the right.
That’s back focus. Your focus is set to a distance further back than your subject. You’re focused behind, or to the back of, your subject. (Front focus is simply where everything’s the other way around.) It’s VERY annoying to shoot your pic of the day of your wife/husband/child/friend and then find out that their face is out of focusbut their ears are tack sharp. Not nice. There are many things that can cause this problem and almost all of them can be chalked up to operator error. Occasionally though, the camera and/or lens is to blame.
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The D70 Human nature is such that when we’re happy with a new toy we tend to simply enjoy it quietly but, if our new toy gives us grief, we want to tell everyone who’lllisten. And some who won’t. So, in evaluating Internet discussions on the back focus issue, one has to be careful not to be misled into believing that every D70 suffers from back focus just because it’s a hot topic. The truth is that only a minority of D70s have been faulty in this regard. The majority work just fine. Why this test? Well, if you’re a new D70 owner and have read all about the trialsand tribulations of other D70 owners who have the dreaded back focus then you probably want to know if YOUR new baby suffers from it or not. Most people who think their D70 has back focus are mistaken. (Please note that I said “most”, not “all”.) In other words, they’re in a tizz for no reason. If they’re having problems then, usually, it’s operator error. This test is intended to help any curiousD70 owners to check their own cameras in order to either heave a sigh of relief that their D70 is fine or to arm themselves with the info needed to return their D70 for exchange or recalibration. Interpreting your results Once you’ve read this all through, assembled your test chart, and have taken a bunch of pics you’ll want to know what they mean. When you view your test pic/s, you should be ableto clearly see that the centre part, or a part close to the centre, is in focus, while the chart gets obviously and progressively more out of focus as you move away from the centre, to the left and right, as in this example:
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If the area that’s in focus is more or less centred around the focal plane of the chart then all is well. If you get something like this next pic, thenyou have back focus:
If you get what you see in this next pic, you have front focus.
Ok, now you need to get on with the assembly of the test chart and take some test pics. Read on.
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WARNING! There are many factors that can lead to erroneous and misleading results when doing this test. Make sure you read the instructions carefully and thoroughly and follow themin detail. Please follow these instructions carefully, paying particular attention to the points dealing with the setup and positioning of the chart and camera. Failure to do this will render the test useless. 1. 2. Print out this document. You should then have: a. These instructions. b. The test chart. c. The cut-out focus box. 3. Additionally, you will need: a. A pair of scissors. b. Glue /paste. c. An old magazine or other source from which to cut out a picture. 4. Cut out the focus box (the last page of this document), and snip off the corners of the fold-down flaps, as in the following picture:
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Crease all the fold lines. First fold over the side flaps:
Then fold over the back panel and the base panel.
Now you can open it all up, apply...